Enhanced Oil Recovery (EOR) may be used to increase oil recovery in fields worldwide beyond what can be achieved by conventional means—possibly extending the life of a field and boosting the oil recovery factor. The three main types of EOR are thermal, chemical/polymer and gas injection.
Thermal enhanced recovery works by adding heat to the reservoir. The most widely practiced form is a steam drive, which reduces oil viscosity so that it can flow to the producing wells. Chemical flooding generally reduces the capillary forces that tend to trap residual oil within the formation. Polymer flooding seals to improve the sweep efficiency of injected water. Miscible injection works in a similar way as chemical flooding. By injecting a fluid that is miscible with the oil, trapped residual oil can be recovered.
Dimethyl ether (DME) may be used for EOR as an aid for removing oil from reservoirs. However, removal of the DME from the produced oil is generally necessary before further processing. In addition, removing the DME from the produced oil can make the DME available for reinjection in a later EOR operation.
In certain methods for removing DME, such as in a water flood operation, DME is finally recovered by means of absorption from gas in water in a counter-current column operation at elevated pressures. Pressure is applied because while at low pressures DME will prefer the gas phase, but when pressures reach or exceed about 10 bar, DME will begin to partition into the hydrocarbon-rich liquid phase. However, at such increased pressures, substantial amounts of low molecular weight hydrocarbons with which DME forms azeotropes, such as propane, isobutane, n-butane and pentane may also partition into the liquid phase. Hence, direct separation with distillation is not feasible.
The conventional approach to recover DME from the hydrocarbon-rich liquid phase that forms during the compression of the produced gas is to use a one-stage or a multi-stage counter-current liquid-liquid (LL) extraction process. A common extraction solvent for counter-current liquid-liquid extraction is water. The approach uses a total draw off tray, taking the water from the wash column, running the water counter-current through an LL-extractor, and sending it to a LL separator. However, in this process, the LL-extractor generally has such a small column diameter that it is not advantageous to combine it with a gas absorption column and LL separator.
In order to overcome the above problems, the present disclosure accomplishes a recovery of DME from a hydrocarbon rich liquid phase into the water effluent of the absorption column and recycling the treated hydrocarbon back to the upstream Gas-Liquid separator to prevent relatively large losses in light hydrocarbons from the oil.